Loosing files in /data folder

[Leong1230]

Hi! Thank you for sharing your great work!
I hava serveral questions:

1. Could you please provide a sample of 'data/US_mask.png', 'data/avg_img.png' and so on? I think it is a mask that segments the fan or rectangle area in the ultrasound images, but I am not sure.
2. data/Demo/Demo_USCalib.txt：Is this the calibration transformation between the ultrasound image coordinate and the probe/tracking marker coordinate? But I couldn't find it used in the paper, am I right?
3. In the paper, the ground truth is the tracking position, not the relative position under the US image coordinate. Why not using the latter as the network output? (Is it because the calibration process brings error to the data?)

Looking forward to your reply! Thank you!